1. Field of the Invention
The present invention relates to probe card technology and more specifically, to a high frequency probe preparation method of making a probe for high-frequency testing.
2. Description of the Related Art
Referring to FIG. 1, a conventional probe for probe card comprises a coaxial cable segment 1 and a probe needle segment 2 bonded to the coaxial cable segment 1 by means of pin connection. According to this design, the configuration of the coaxial cable segment 1 keeps impedance matching for signal transmission by avoiding signal attenuation. Thus, the probe is practical for the application of high-frequency transmission.
However, the pin connection between the coaxial cable segment 1 and the probe needle segment 2 tends to cause a signal discontinuous interface, i.e., signal transmission non-integrity.
To avoid the aforesaid problem, a high-strength probe needle segment may be used as a core member for further processing to make a coaxial cable type probe needle that provides impedance matching for signal transmission and eliminates the problem of signal discontinuity. U.S. Pat. No. 6,727,716 discloses a similar design, entitled “Probe card and probe needle for high frequency testing”. According to this design, the high frequency probe needle 630 comprises a conductor 640, a dielectric sleeve 650 surrounding at least a portion of the conductor 640, and a conductive cover 652 surrounding the dielectric sleeve 650. Thus, the high frequency needle 630 can be prepared without pin connection, eliminating the problem of signal transmission non-integrity.
However, during preparation of the probe needle 630, it is necessary to make the conductive cover 652 and the dielectric sleeve 650 at first, and then to sleeve onto the conductor 640. Inevitably, the structure of the conductive cover 652 and dielectric sleeve 650 will be bent somehow in the step of sleeving the conductor 640. Further, when the end of the probe needle 630 is pressed on the electronic device to be tested during operation of the probe card, the cantilever part of the probe needle 630 will be curved, too. If the conductive cover 652 does not have excellent bending extensibility, the conductive cover 652 may be forced to crack and even to drop from the dielectric sleeve 650 during bending of the structure of the conductive cover 652 and dielectric sleeve 650. By the way, the bending extensibility of the conductive cover 652 is inverse proportional to its thickness. According to this design, the conductive cover 652 has a thickness over 1.5 mils, or about 38.1 μm. In practice, the thickness of the conductive cover 652 is excessively high, and the bending extensibility of the conductive cover 652 is insufficient to prohibit the conductive cover 652 from cracking when forcing the probe needle 630 to touch the device, thereby affecting signal transmission performance. Moreover, the thickness of the conductive cover 652 has a great concern with the total thickness of the probe needle 630. Since the conductive cover 652 has an excessively high thickness, the probe needle 630 will not be practical for fine pitch devices under high frequency test, thus limiting the application of the probe needle 630.
Therefore, it is desirable to provide a high frequency probe needle that eliminates the aforesaid problems.